This application relates to the art of slack adjusters and, more particularly, to automatic slack adjusters for adjusting vehicle brakes. Although the invention will be particularly described with reference to adjustment of vehicle brakes, it will be recognized that the slack adjuster assembly may be used for adjusting other devices.
One type of vehicle brake is operated by rotating a slack arm back and forth in brake apply and brake release directions to rotate a cam shaft which cooperates with brake shoes for moving same between engaged and disengaged positions. As the lining on the brake shoes wears, it is necessary to rotate the cam shaft to a new position relative to the slack arm for achieving a maximum braking force when the slack arm moves through a predetermined stroke. The most common mechanism for rotatably adjusting the cam shaft relative to the slack arm includes a worm wheel drivingly connected to the cam shaft, and positioned between the cam shaft and the slack arm. A worm gear carried by the slack arm engages the worm wheel for rotating same in unison with the slack arm during normal operation. A reciprocating mechanism is operative upon overtravel of the slack arm to rotate the worm gear relative to the slack arm for rotatably driving the worm wheel and cam shaft relative to the slack arm to a new adjusted position. Mechanisms of this type are relatively expensive and complicated due to the use of worm gears and worm wheels. It would be desirable to have a mechanism for effecting an adjustment without requiring the use of worm gears and worm wheels, along with the relatively complicated and expensive reciprocating mechanism for driving the worm gear.